The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Ratio of sulfuric acid to water for anodizing

I am new to anodizing. What is the correct formula to know how much sulfuric acid to add to the water to get the right percentage? I am using 66 sulfuric and De-ionized water.

Mike Davis
hobbyist - Kalispell, MT, USA
September 2, 2008

---

You need some specifications. If you are going to use 15% by weight sulfuric and sulfuric specific gravity is about 1.6 of water, you would divide the 15% by 1.6 and get about 9.4 gal of acid per 100 gal of total solution.
You need to add the acid to the water very slowly with protective equipment. It will get extremely hot, so plan on it taking a couple of days. If you need it faster, you could use a bit of ice in place of some of the water. If this is a tiny setup, make the ice out of DI water.
Stir very well and then come back after it has cooled and stir again. Then sample and test for the % of acid. I never seems to come out exact, so leave the liquid level a couple % below the desired level of the tank. This will allow you to add acid or water as required.
Get the analytical capability before you make up the tank. Have your test methods in print. You will also need to test for the amount of aluminum in the solution as you use it.
Do you have a chiller for your system. You need one if you are going to make more than one run of parts a day or if the parts have a large surface area.
I hope that you are not planning to use a battery charger for your power source.

James Watts
- Navarre, Florida
September 5, 2008